Rice Sheath Blight

The causative agent of the disease is the fungus Rhizoctonia solani, as well as the species R. oryzae and R. oryzae-sativae. The genetic anastomosis group AG-1 IA poses the greatest threat to the crop. The infection affects the aerial parts of the plant, starting from the leaf sheaths at the tillering or internode elongation stage. Initial symptoms appear as oval or elliptical green-gray spots, which, as they progress, develop a grayish-white center with a dark brown border.

Pathogen development is favored by high air humidity (over 95%) and temperatures in the range of 30–32°C. Under these conditions, the fungus spreads rapidly to the upper leaves and panicles, causing crop lodging and significant yield losses. Sclerotia form on the affected tissues, which detach easily and persist in the soil as the primary source of subsequent infection.

Rice resistance to sheath blight is a complex polygenic trait, which complicates the breeding of varieties with complete monogenic resistance. The classification of the pathogen into races is difficult due to its high variability and its nature as a polyphage; therefore, current research is focused on the analysis of genetic markers for quantitative resistance and the study of plant immune system mechanisms.